This invention relates to waste conversion, and more particularly, to a system utilizing solid, liquid or sludge waste along with waste gas to generate electricity.
Industries such as the petrochemical industry generate substantial amounts of waste material that could be used for electricity generation, but is often not so utilized. Such waste typically includes solid, liquid or sludge waste, along with waste gas such as pentane. Oftentimes, the pentane is flared-off thereby wasting its energy content. Previous technologies have not been fully able to take advantage of the electricity generating capability of the wide-range of waste that is available. It is desirable to use both gaseous and non-gaseous waste to produce electricity, and to produce such electricity with the highest possible efficiency.
Previous technologies such as that disclosed in U.S. Pat. Nos. 5,847,353 and 6,066,825, the contents of which are incorporated herein by reference, disclosed the use of waste conversion apparatus to convert waste material into hydrogen-rich gas, which was then converted into electricity in a lean burn reciprocating engine producing electricity at high efficiency with low generation of nitrogen oxides. A significant amount of energy, however, is lost in the conversion of the waste into hydrogen-rich gas, thereby lowering overall efficiency. An objective of the present invention is to reduce the amount of waste that is converted into hydrogen-rich gas to increase efficiency.
The waste conversion system according to one aspect of the invention includes a source of solid, liquid or sludge waste along with a source of waste gas. A waste conversion device receives the solid, liquid or sludge waste and converts it into a hydrogen-rich gas. An internal combustion engine receives as fuel the hydrogen-rich gas and the waste gas. A generator is operatively connected to the internal combustion engine to generate electricity. In one embodiment, at least a portion of the waste gas is also converted into hydrogen-rich gas. In another embodiment, the system further includes a water shift reaction chamber for receiving the hydrogen-rich gas to convert it into additional hydrogen and carbon dioxide for subsequent delivery to the internal combustion engine.
In a preferred embodiment, the waste conversion device is a Plasma Enhanced Melter(trademark) which may receive electricity from the generator for its operation. The system of the invention may be operated such that the ratio of energy contained in the hydrogen-rich gas to energy contained in the waste gas is in the range of 0.1-0.5. It is preferred that the internal combustion engine be operated at an equivalence ratio in the range of 0.3-0.7, and at a compression ratio in the range of 10-15. In a particularly preferred embodiment, the solid, liquid or sludge waste is K and F Waste and the waste gas is a pentane containing gas. The waste gas may also include syngas produced by the refinery process.
The present invention provides a more efficient approach to utilizing waste to generate energy because only a fraction of the waste is converted into the hydrogen-rich gas. Typically, only the solid, liquid or sludge is converted to hydrogen-rich gas; in some cases, a portion of the waste gas may also be converted into additional hydrogen-rich gas if necessary to assure stable lean burn operation. The addition of the hydrogen-rich gas to the waste gas enables lean operation of the internal combustion engine and increases the efficiency of electricity generation.
An important application of the technology disclosed herein is the extraction of energy from waste sludges and pentane containing gases produced by oil refineries as part of the refining process. The solid waste serves as the primary source of hydrogen-rich gas and this hydrogen-rich gas enables higher efficiency electricity generation using waste gas such as a pentane containing gas. The system of the invention therefore minimizes the amount of waste converted to hydrogen-rich gas.